Present day position systems use the Global Positioning System (GPS) to provide the position of a vehicle (matted herein as “(X, Y, Z)”). The GPS has inherent inaccuracy. The error of a typical GPS receiver can be up to 10 metes. In addition, two GPS receivers, located in proximity, may have different errors resulting from different selection of satellites or different processing orders of satellite signals.
The GPS performance degrades when line-of-sight (LOS) is unavailable. No GPS signal is available inside buildings (such as indoor parking lots) and in tunnels. Skyscrapers also block the GPS signal. In cases like this, non-GPS based location techniques such as dead-reckoning are applied. Dead-reckoning is based on accelerometer or gyroscope information or using vehicle movement information in more advanced systems. The dead-reckoning error increases with usage time. Dead-reckoning can provide approximate positioning for a short period of time, but is ineffective after long usage. GPS improvements include differential GPS (DGPS), which utilizes a tall antenna as a point of reference. All GPS components today support DGPS, which brings the error down to 3 meters. However, the problems of blocked, GPS signals are not solved by this solution.
A major use of position information is in safety applications. While GPS provides a sufficient level of accuracy for navigation purposes, this level of accuracy is not acceptable for supporting safety applications. For example, for reliable safety indications to drivers, the relative accuracy needs to be less than about 1 meter and preferably less than about 0.5 meters. Some cases in which improved position accuracy is needed include:
Obtaining lane specific information—a vehicle braking indication needs to be processed mostly by vehicles in same lane.
Obtaining lane function information—a vehicle driving in a special purpose lane, such as a crossing or a turning lane, needs to be treated differently than vehicles driving in other lames.
Close proximity positioning—exact positioning is critical for determining a probable collision.
Absolute positioning—using a fixed device in a known place, like a Road Side Unit (RSU) in positions with bad GPS signal reception.
Mobility—lane based information can improve mobility estimation.
In summary, in safety applications, the relative positioning between two vehicles has higher importance than absolute global positioning.
Cooperative safety systems based on vehicle-to-vehicle communication show great promise to reduce the traffic accidents and fatalities. Therefore, there is a need for, and it would be advantageous to have, an improved relative positioning system and method to increase relative position accuracy and, consequently, vehicular safety.